1. Field of the Invention
The present invention relates to a control apparatus for an electric rotating machine, the control apparatus being configured to control the controlled variables of the electric rotating machine by adjusting the output voltage of a power converter circuit including switching elements which are operated to connect positive and negative terminals of a DC power source to corresponding terminals of the electric rotating machine.
2. Description of Related Art
Such control apparatuses include the one which performs triangular wave comparison PWM control in which, in order to feedback-control the currents flowing through the respective phases of a three-phase motor at their command values, command voltages of the respective phases are calculated, and switching elements of an inverter are operated in accordance with comparison results between each of the calculated command values and a triangular wave carrier signal.
Further, in recent years, there is proposed the one which performs the so-called model predictive control in which the currents flowing through the respective phases of a three-phase motor are predicted for each of different operating states of an inverter, and the inverter is operated in one of the operating states in which the deviation between each predicted current and a command current is minimum. For example, refer to Japanese Patent Application Laid-Open No. 2008-228419 (Patent document 1). According to the above apparatus, since the inverter is operated such that the behavior of the currents predicted on the basis of the output voltage of the inverter is optimized, the followability to the command current during a transient period can be improved compared to the apparatus which performs the triangular wave comparison PWM control. Accordingly, the model predictive control is expected to be useful for a control apparatus which is required to exhibit high followability during a transient period, for example, when it is used for a motor-generator which is mounted on a vehicle as a main engine of the vehicle.
Incidentally, such a control apparatus which performs the model predictive control is described also in Japanese Patent No. 3727268 (Patent document 2).
However, in the control apparatus which performs the model predictive control, although the output current of an inverter can be controlled at a command current within the range in which the modulation index is smaller than 1, that is, an average amplitude between output lines of the power converter circuit is smaller than the voltage of the DC power source, it is difficult to control the output current at the command value in the overmodulation range in which the modulation index exceeds 1 due to the constraint depending on the input voltage of the inverter.